System for inspecting matt, flat and/or slightly curved surfaces

ABSTRACT

A system for inspecting matt, flat and/or slightly curved surfaces in order to identify defects includes an illumination device which irradiates the surface to be inspected at flat angles and has the following features. The illumination device is formed from a plurality of elongated luminous surfaces which are disposed substantially parallel to one another. The light distribution of the respective elongated luminous surfaces is tightly concentrated in planes which lie transversely with respect to the longitudinal direction of the respective surface, in such a way that a substantially sheet-type light distribution is produced which covers the surface portion to be inspected. The observer is located within or at least in the proximity of the angle predetermined by reflection of the light radiated by the at least one elongated luminous surface on the surface portion to be inspected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a system for inspecting matt, flat and/orslightly curved surfaces in order to identify defects which areassociated with a modification of the course of the surface, especiallyfor checking flat/unlacquered shell bodywork.

2. Discussion of Related Art

Systems for inspecting matt, flat and/or curved surfaces in order toidentify surfaces are known, which have surfaces radiating strip-shapedlight, by means of which surfaces unlacquered metal and plasticsmaterial surfaces are sampled for topographical defects in a directionparallel with the surface. This requires incident light radiation atvery flat radiation angles of approximately 5 to 10°, because at theseangles the surfaces reflect in a very directed manner, whilst at steeperangles they predominantly reflect in a diffuse manner. Such illuminationstrips are suitable only for small surface portions, or means have to beprovided with which the strips can be moved relative to the surface (WO98/15815). If, however, a plurality of strips are lined up beside oneanother to illuminate larger surfaces, surface portions of the surfaceto be sampled which are located closer to the lights are illuminated atundesirably steep angles. This leads to masking of defects andidentifiable colours and colour effects which would normally berecognisable when associated with the luminous strip. Furthermore theproblem of direct dazzling occurs since the lights do not only radiatein the desired directions onto the surface as a result of their lightdistribution which is too wide.

OBJECT OF THE INVENTION

The object underlying the invention, therefore, is to create a systemfor inspecting matt, flat and/or slightly curved surfaces which alwayscreates the same illumination conditions over a surface of any size tobe sampled, the light distribution of the illumination being intended tobe suitable for making topographical defects of an otherwise continuoussurface clearly recognisable, the light radiation being intended to belimited to the solid angle required to illuminate the surface, in orderto avoid dazzling when the light-radiating surface is viewed directly.At the same time, the luminous device used should be simple in itsstructure.

This object is accomplished according to the invention by the featuresof the main claim.

BRIEF SUMMARY OF THE INVENTION

According to the invention the illumination device comprises a pluralityof elongated luminous surfaces, disposed substantially parallel to oneanother and possessing substantially all the same light distribution,which is tightly concentrated in planes which lie transversely withrespect to the longitudinal direction of the surfaces, with an apertureangle which is smaller than 15°, preferably 5°, and by even greaterpreference smaller than 2°, such that a substantially sheet-form lightdistribution is produced which covers the surface element to beinspected on the surface. In planes in the longitudinal direction of thesurfaces, the illumination device has in each case a widely radiatinglight distribution. The illumination device is so disposed that theangle between the normal line of the inspected surface element and theconnecting line between the inspected surface element and any point onthe elongated luminous surface is greater than roughly 60°, preferablyhowever 75°, and the observer, i.e. a person or a camera or the like, islocated within or at least in the proximity of the at least oneelongated strip illuminating by reflection of the sheet-type lightdistribution on the surface portion to be inspected. By means of thissystem, illumination is achieved which does not cause any inadvertentdazzling when the light-radiating surfaces are viewed directly, andwhich permits good detectability of defects which are connected with amodification of the course of the surface.

With the same illumination principle, the position of the observer canbe altered by optical means such as mirrors, retro-reflective foils orprisms.

Through the measures quoted in the subordinate claims, advantageousdevelopments and improvements are possible.

Preferably the illumination device used has a light-radiating originalsurface, in front of which a bundle with parallel lamellae surfaces isdisposed, the main radiation direction of the original surface radiatinglight through the lamellae arrangement. The original surface has uniformluminance distribution and radiates light in a larger solid angle areathan the totality of the elongated light-radiating surfaces at the endof the lamellae bundle. The lamellae arrangement is preferably sodimensioned in respect of its geometry, i.e. spacing and depth, thatdiagonally to the lamellae surface the aperture angle is smaller than15°, preferably smaller than 5°, and by particular preference smallerthan 2°.

The original surface is preferably formed by elongated light sourceslying beside one another or also by at least one elongated light sourcewhich is surrounded by a trough-like reflector. The elongated lamps canbe for example fluorescent lamps or linear incandescent lamps, the lightdistribution of which is automatically widespread in planes parallel tothe lamp axis. It is propitious to use only a few lamps and so to aligntheir light distribution by reflectors or lenses that the solid angleregion over which the radiation falls is greater than the solid anglerequired by the entire illumination device.

According to the invention, the surfaces of the lamellae scatter lightin a diffuse manner with a is smaller proportion of directed reflection,or they reflect in a directed manner with a small reflection factor. Agap-free illumination in a narrow angle range is produced according tothe invention with surfaces which at very flat incident light angleshave a high degree of directed reflection and at steeper incident lightangles pass into diffuse reflection. These are, for example, lacqueredsurfaces or metallic surfaces. The surfaces of the lamellae arepreferably black or grey.

In a preferred embodiment, the lamellae can also be disposed either onone or on both sides of light guide plates so as to be optically dense,filling the gaps between the plates and having polished light entranceand exit surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are represented in the drawing and aredescribed in greater detail in the following description. The figuresshow:

FIG. 1: a schematic front elevation of the system according to theinvention,

FIG. 2: a perspective view of an illumination device which is used inthe system according to the invention,

FIG. 3: a section through a further embodiment of an illuminationdevice, as is used in the system according to the invention,

FIG. 4: a representation of light distributions, as used in anillumination device according to the invention,

FIG. 5: the representation of a sheet-type light distribution accordingto FIG. 4,

FIG. 6: ray paths at the lamellae used in the illumination deviceaccording to the invention, and

FIG. 7: ray paths according to FIG. 6 at other angles of incidence.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 is represented a system for inspecting the side surfaces ofshell bodywork 1, in which system at least one illumination device 2illuminates a flat or slightly curved surface 3, which is roughlyperpendicular in the embodiment shown, and an observer 4 inspects theilluminated surfaces for defects which are connected with a modificationof the course of the surface, i.e. topographical defects. The observercan here be a person; a camera or some other sensor arrangement fordetecting the image of the surface can also be provided. Illumination bythe illumination device 2 takes place at a flat angle smaller than 30°,and preferably smaller than 15°, i.e. greater than 60° to the normalline of the surface 3, preferably greater than 75°. The observer 4 islocated within or in the proximity of the angle predetermined by thereflection of the light rays of the illumination device 2, i.e.approximately in the mirror angle. The illumination device 2 isrepresented in various embodiments in FIGS. 2 and 3, the lightdistribution of the illumination device being recognisable in FIGS. 4and 5. The illumination device 2 has a plurality of elongated luminoussurfaces 5 lying beside one another, which together form the light exitsurface 6 of the illumination system 2. The longitudinal direction ofthe luminous surfaces 5 is perpendicular in FIG. 1 to the page plane,and in an identical longitudinal direction, i.e. in a longitudinaldirection parallel to the longitudinal direction of the luminoussurfaces 5, lies the surface to be inspected 3. The light distributionof each luminous surface 5 is represented in FIG. 4 and FIG. 5, thelight distribution 7 showing the radiation in planes which lietransversely with respect to the longitudinal direction of the luminoussurface 5, whilst the light distribution 8 represents the widespreadradiation in planes in the longitudinal direction of the luminoussurface 5. One surface element 9 of the luminous surface 5 isrepresented in FIG. 5 in a small x-, y- and z-coordinate system, whichdelivers a light distribution according to FIG. 4. Here z represents thelongitudinal direction and it can be recognised that the light istightly concentrated in planes which lie transversely with respect tothe longitudinal direction, such that a substantially sheet-type lightdistribution 10 is produced. Here the aperture angle in the planes whichlie transversely with respect to the longitudinal direction is smallerthan 15°; an aperture angle of smaller than 5° is better, howeverpreferably smaller than 2°.

The luminous surfaces 5, as shown in FIG. 1, have such a sheet-typelight distribution 10, the light thus being radiated in narrow stripsonto the surface 3. These narrow strips lie on the surface 3transversely with respect to the longitudinal direction of the surface,and they preferably only overlap one another slightly. The strips areviewed by the observer 4 at an angle which deviates slightly from themirror angle but is in the vicinity of same since in this casetopographical details can be recognised even better.

In FIG. 2 is represented an illumination device 2, the luminous originalsurface 11 of which is formed from a plurality of lamps 12 alignedparallel to one another and at a small spacing from one another. Theluminous original surface 11 has a uniform luminous distribution, thelamps being for example elongated fluorescent lamps or linearincandescent lamps. In front of the lamps is disposed a plurality oflamellae 13 aligned parallel and forming a lamellae bundle, which as aresult of their geometry, i.e. their mutual spacing and their depth,form the desired aperture angle of smaller than 15°, better 5°,preferably 2°.

In FIG. 3 is represented a further embodiment of the illumination deviceused in FIG. 1, and this in section, an elongated light source 14 alsobeing used here which is surrounded by a reflector which is configuredtrough-like for example. Here the inner side of the reflector 5 facingthe lamp 14 forms the original surface, the luminance of which isuniformly distributed. In front of the reflector 5 is arranged again abundle of lamellae 13, the aperture angle of a luminous surfacecorresponding to the light distribution according to FIG. 5 being givenby the light rays 16. The illuminated surface is in this caseinterrupted again and again in oblique directions by the lamellae 13.

FIG. 6 shows a continuously illuminated light-radiating surface 6,formed from two partial surfaces, between the lamellae 13, of which onlythree are shown here. This uniform light-radiating surface 6 is producedby directed reflection of the light rays 17, 18 at the lamellae 13 atflat angles, such that the surface to be inspected is also illuminatedwithout any gaps.

In FIG. 7, on the other hand, steeper light rays 19, 20 are represented,from the direction of which the lamellae optical system now appearsdark. Rays 19 and 20 are produced by multiple reflections of rays 21 and22, which moreover impinge at steeper angles of light incidence, atwhich the degree of the directed reflection decreases, such that rays 19and 20 have practically no luminance anymore. This means that theobserver 4, if he inadvertently looks directly into the illuminationdevice 2 according to FIG. 1, is not dazzled. The surfaces of thelamellae are preferably black.

In a further embodiment of the illumination device, for exampleaccording to FIG. 3, between the lamellae 13 are provided light-guidingtransparent plates, i.e. the gaps between the lamellae 13 are filledwith a light-guiding transparent medium, the lamellae surface beingconnected at least on one side in an optically dense manner to thetransparent medium or respectively the light guide plates. Here thelight guide plates have polished light entrance and exit surfaces.

The abstract forms part of the disclosure of the present invention, i.e.part of the description.

What is claimed is:
 1. A system for inspecting matt, flat and/orslightly curved surfaces in order to identify defects which areassociated with a modification of the course of the surface, inparticular for examining matt unlacquered shell bodywork, in whichsystem an illumination device irradiates the surface to be inspected atflat angles, said device having the following combined features: theillumination device is formed from a plurality of elongated luminoussurfaces which are disposed substantially parallel to one another, theangle between the normal line of an inspected surface element on thesurface and the connecting line between the inspected surface elementand a point on one of the elongated luminous surfaces is greater thanapproximately 60°, the light distribution of the respective elongatedluminous surfaces is tightly concentrated in planes which lietransversely with respect to the longitudinal direction of therespective surface, with an aperture angle which is smaller than 15°, insuch a way that a substantially sheet-type light distribution isproduced which covers the surface portion to be inspected, and theobserver is located within or at least in the proximity of the anglepredetermined by reflection of the light radiated by the at least oneelongated luminous surface on the surface portion to be inspected.
 2. Asystem according to claim 1, wherein the aperture angle of thesheet-type light distribution is smaller than 5°, preferably smallerthan 2°.
 3. A system according to claim 1, wherein the angle between thenormal line of an inspected surface element and the incident light rayof the elongated luminous surface is greater than 75°.
 4. A systemaccording to claim 1, wherein the longitudinal direction of the luminoussurfaces is substantially parallel to the longitudinal direction of thesurface to be inspected which is illuminated by this luminous surface.5. A system according to claim 1, wherein each surface portion to beinspected is illuminated by at least one elongated luminous surface fromits entire length and breadth.
 6. A system according to claim 1, whereinthe luminous elongated surfaces so disposed beside one another are soarranged in respect of their concentration that they illuminate adjacentsurfaces to be inspected in the same alignment.
 7. A system according toclaim 1, wherein the illumination device has a light-radiating originalsurface which has a substantially uniform luminance distribution andwherein there is arranged in front of this original surface a pluralityof lamellae which are substantially parallel to one another and whichdetermine the desired aperture angle on the basis of their geometry. 8.An illumination device according to claim 7, wherein the surfaces of thelamellae have a high reflection factor of the directed reflection atflat light entrance angles, and at steep light entrance angles reflectpredominantly in a diffuse manner.
 9. A system according to claim 7,wherein the surface of the lamellae is black.
 10. A system according toclaim 7, wherein the gaps between the lamellae are filled with alight-guiding transparent medium, and in that the surface of thelamellae is connected to the medium in an optically dense manner atleast on one side.
 11. A system according to claim 1, wherein theobserver is a person, a camera or some other sensor arrangement forcapturing an image.
 12. A system according to claim 1, wherein theillumination device has a light-radiating original surface which has asubstantially uniform luminance distribution the light-radiatingoriginal surface radiating at a solid angle which is greater than thesolid angle of the radiation of the luminous surfaces.
 13. A systemaccording to claim 1, wherein the illumination device has at least oneelongated light source, the light distribution of which radiates widelyin planes parallel to its axis.
 14. A system according to claim 1,wherein the illumination device has a light-radiating original surfacewhich has a substantially uniform luminance distribution whereby theoriginal surface is composed of a plurality of widely radiating,elongated light sources which are disposed beside one another, at leastone pair of lamellae being placed in front of each light source.
 15. Asystem according to claim 1, wherein the illumination device has alight-radiating original surface which has a substantially uniformluminance distribution the original surface being formed from at leastone elongated light source with a trough-like reflector.
 16. A systemaccording to claim 1, wherein the position of the observer can bealtered by optical measures such as mirrors, retro-reflective materialsor prisms.